Hajj, the pilgrimage to Mecca, Saudi Arabia, is one of the five basic requirements (arkan or "pillars") of Islam. Its annual observance corresponds to the major holy day Eid al-adha, itself a commemoration of Abraham's readiness to sacrifice his son on Divine orders. While the Hajj is a religious obligation to be fulfilled at least once in the course of the life of each Muslim, religious law grants many exclusions on grounds of hardship.

Hajj is a series of extensively detailed rituals. These include wearing a special garment that symbolizes unity and modesty, collective circumambulations of the Kaaba, and the symbolic stoning of evil. A central event of the pilgrimage is at the station on the plain of Arafat, some ten miles from Mecca, where, massive crowds notwithstanding, the pilgrim is required to be completely alone with God performing the rite of wuquf or "standing." It is here that the Prophet Muhammad (pbuh) addressed his followers during his last pilgrimage.

The Mecca rituals are customarily followed by a visit to the Prophet's Mosque in Medina. The Hajj, today gathering millions of Muslims annually, was perhaps the greatest impetus to voluntary mobility before modern times. The economic, cultural, and political importance of this major annual gathering of Muslims from around the world has further increased with the advent of telecommunications and transport technologies, though the increased numbers have taxed the available facilities. Those who have completed the pilgrimage are entitled to add the phrase al-Hajj or Hajji (pilgrim) to their name.